Hello,
I have few questions regarding G1 RSets.
We are running java on a 30Gb machnie with Xmx=20Gb, howewer, java managed
to use extra 7.5Gb above that 20Gb. According to NMT, the most significant
sources of memory consumptions are:
Java Heap (reserved=20971520KB, committed=20971520KB)
(mmap: reserved=20971520KB,
committed=20971520KB)
GC (reserved=3021667KB, committed=3021667KB)
(malloc=2210659KB #61926090)
(mmap: reserved=811008KB, committed=811008KB)
Internal (reserved=2358976KB, committed=2358976KB)
(malloc=2358944KB #1205678)
(mmap: reserved=32KB, committed=32KB)
Assuming that most of the memory is claimed by G1, I've added an option to
track what is RSet consumption stat is:
Current rem set statistics
Total per region rem sets sizes = 2803150K. Max = 2448K.
128K ( 0.0%) by 13 Young regions
76K ( 0.0%) by 7 Humonguous regions
8874K ( 0.3%) by 898 Free regions
2794071K ( 99.7%) by 1642 Old regions
Static structures = 290K, free_lists = 11539K.
2878842478 occupied cards represented.
0 ( 0.0%) entries by 13 Young regions
47 ( 0.0%) entries by 7 Humonguous regions
0 ( 0.0%) entries by 898 Free regions
2878842431 (100.0%) entries by 1642 Old regions
Region with largest rem set =
75:(O)[0x00000002e5800000,0x00000002e6000000,0x00000002e6000000], size =
2448K, occupied = 1687K.
Total heap region code root sets sizes = 114K. Max = 29K.
0K ( 0.2%) by 13 Young regions
0K ( 0.1%) by 7 Humonguous regions
14K ( 12.2%) by 898 Free regions
100K ( 87.5%) by 1642 Old regions
3010 code roots represented.
0 ( 0.0%) elements by 13 Young regions
0 ( 0.0%) elements by 7 Humonguous regions
0 ( 0.0%) elements by 898 Free regions
3010 (100.0%) elements by 1642 Old regions
Region with largest amount of code roots =
147:(O)[0x0000000309800000,0x000000030a000000,0x000000030a000000], size =
29K, num_elems = 1.
, 0.6920868 secs]
Looks like half of this 7Gb extra is cards and bitmaps for RSet. So my
questions are:
- Is there any information about internal implementation details available
anywhere?
- Is there a way to estimate what overhead would be and how this is
related to app memory footprint?
- In our app it's mostly strings and we are using strings deduplication,
could it be the problem, since it creates extra references between regions,
increasing footprint for RSet?
Thanks,
Stas
_______________________________________________
hotspot-gc-use mailing list
hotspot-gc-use@openjdk.java.net
http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
